Embodiments of the invention relate generally to a microelectromechanical system (MEMS) switch having a conductive mechanical stop.
Microelectromechanical systems (MEMS) are electromechanical devices that generally range in size from a micrometer to a millimeter in a miniature sealed package. A MEMS device in the form of a microswitch has a movable actuator, also referred to as a beam, that is moved toward a stationary electrical contact by the influence of a gate or substrate electrode positioned on a substrate below or otherwise near the movable actuator. The movable actuator may be a flexible beam that bends under applied forces such as electrostatic attraction, magnetic attraction and repulsion, or thermally induced differential expansion, that closes a gap between a free end of the beam and the stationary contact.
FIG. 1 illustrates a cross-sectional representation of a MEMS switch in an open or non-conducting state according to the prior art. The MEMS switch 10 includes a substrate 12, an insulating layer 14 disposed over the substrate 12 and a movable actuator 23 mechanically coupled or anchored to a source electrode 18 as shown. The movable actuator 23 includes a movable contact 17, which upon deflection of the movable actuator 23 makes contact with a substrate contact 15 disposed on but electrically isolated from the substrate 12. The substrate electrode 16 is positioned below the movable actuator 23 such that when an actuation voltage is applied to the substrate electrode 16, the movable actuator 23 deflects such that contact is made between the movable and stationary (e.g., substrate) contacts to allow current to flow. In order to keep the conductive movable actuator 23 from contacting the substrate electrode 16 and electrically shorting the switch when in such a conducting state, a dielectric layer 20 is typically coated over the substrate electrode 16 as illustrated in FIG. 2. This dielectric layer is often disposed over the substrate electrode 16 but it may instead be coated on the underside of the movable actuator 23.
However, such a dielectric insulation layer can trap charge over time and negatively affect the operation of the actuator such as causing it to malfunction (e.g., cause stiction of the electrode), change the actuation and stand-off voltages, change the response time of the switch, shorten its operating lifetime, and so forth. This can be especially problematic in power conduction applications where inadvertent actuation can cause undesirable conduction modes and/or switch damage.